Research On The Distribution And Tectonic Characteristics Of The Mesozoic Strata Of The East China Sea Shelf Basin

The East China Sea Shelf Basin is located on the east Asia continental margin. It is aMesozoic-Cenozoic composite basin superposed on the South China Block. The research area islocated on southern of East China Sea Shelf Basin composed of Oujiang Sag, Yandang Heave,Minjiang Sag, Taibei Heave, Jilong Sag, Taixi Basin and Xinzhu Sag, with an area of12×104km2.Due to previous studies focus on the Cenozoic strata and tectonic, the Mesozoic strata andtectonic characteristics is not clear, which constrict understanding the Mesozoic tectonicframework and geodynamic process of South China continent. Based on the above problems, thispaper fully collect the Mesozoic geological literature, engage in the Mesozoic outcrop field trip toZhejiang Province and Fujian Province, and participate in16000km2D seismic profilesinterpretation work. The research work includes: establishing the sequence stratigraphicframework; obtaining formation thickness and subsidence migration patterns; dividing tectonicunits, analyzing the characteristic of the faulting system and its control of the tectonic units；clarifying the superposition of different tectonic stress fields by tectonic style inversion；magmaage statistics and summarizing the magma migration patterns；understanding tectonic deformationfeatures in different evolutionary stages by balanced section construction and quantitativerecovery; analysis of tectonic evolution and history of basin filling and Mesozoic prototype basinrestoration. The main achievements are as following:1. The Mesozoic strata developed well in land area of South China Block after the Indosinianmovement. There are three main regional unconformity in the eastern land area of ZhejiangProvince, Fujian Province, and Guangdong Province, e.g. the unconformity between middleJurassic and and late Jurassic, the unconformity between early and late early Cretaceous, and theunconformity between late Cretaceous and Paleogene. The three unconformity correspond to threeorogenic movement of Yanshan epoch.2. On the seismic profiles of southern East China Sea Shelf Basin, six seismic reflectionwaves can be identified, e.g. T20, T30, T40, T50, T60and Tg. The T20, T40, T50, T60and Tgare fiveunconformity surface, corresponding to Quaternary-Neogene, Paleogene, Cretaceous, Jurassic andpre-Mesozoic.3. The Mesozoic strata distribute in NE orientation totally in study area. In the Oujiang-Lishui sag belt, the Cretaceous strata have a thickness of1000-2500m, with a maximumresidual thickness of up to3000m. The Cretaceous strata has a residual thickness of400-1500m innorthern Yandang low Heave belt and200-800m in southern. The Jurassic and Cretaceous strata inMinjiang-Xiapeng slope belt are about2000-5000m thick, with a maximum thickness of5500m.The Jurassci and Cretaceous strata are developed extensively in Jilong-Xinzhu Sag belt. TheMesozoic thickness is about3000-7000m, with a maximum thickness of up to8000m. Thesedimentation center migrate from the west to the east in Mesozoic Epoch.4. Through regional sea-land contrast, the paper put forward that the Xiamen Formationbelong to middle Jurassic, the possible loss of volcanic-sedimentary formation during late Jurasscito early Cretaceous in the East China Sea Shelf Basin.5. According to sedimentary characteristics and deformation characteristics, the Mesozoicbasin of East China Sea Shelf Basin can be divided into four secondary Mesozoic tectonic units,e.g. Oujiang-Lishui Sag belt, Yandang low Heave belt, Minjiang-Xiapeng slope belt andJilong-Xinzhu Sag belt. There mainly develop NE-NNE orientation fault and four kinds oftectonic style in Mesozoic epoch. The East China Sea Shelf Basin mainly experienced JilongMovement, Yushan Movement and Yandang Movement, roughly corresponding to the IndosinianMovement, Yanshan II phase Movement and Yanshan III phase Movement in South China Block.6. Through the interpretation of seismic profiles, the paper reture to the boundary of theJurassic and Cretaceous prototype basin, the Jurassic for depression basin and cretaceous for faultdepression basin.7. Through the structural evolution section recovery and combined with regional sea-landtectonic contrast, the Mesozoic evolution process is divided into three stage: the passivecontinental margin depression stage in the late Triassic-middle Jurassic, the Andean activecontinental margin arc uplift stage in the late Jurassic-early Cretaceous, and the West Pacificactive continental margin back-arc stretch basin stage in the late early Cretaceous-late Cretaceous.